[Autofill Assistant] Don't show UI after moving tabs when feature is off

Before this change with tab-switching turned off if a script was
running when the user chose "Open in Chrome" from CCT, the UI would
move from CCT to a normal tab, even with the tab-switching feature
turned off.

What should instead have happened is AA shutting down. However, AA
takes a while to shut down when a script is running,

This patch prevents the UI from showing again on the new tab, after it's
been taken out of CCT. It also forces prompt and PR actions to terminate

Bug: b/128666286
Change-Id: Ie89f7062e480322b45132ff44ee3f8b1cdb1b9c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1524359
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Commit-Queue: Stephane Zermatten <szermatt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641838}
13 files changed